Combustion chamber construction in a gas turbine engine



H. G- HILL Jan. 28, 1958 COMBUSTION CHAMBER CONSTRUCTION IN A GAS TURBINE ENGINE Filed May 28, 1956 INVENTOR. HEN/ V a l/ALL ATTORNEY? COMBUSTION CHAMBER CONSTRUCTIQN IN A GAS TURBlNE EN GM Henry C. Hill, Seattle, Wash, assignor to Boeing Airplane Company, Seattle, Wash, a corporation of Delaware Application May 28, 1956, Serial No. 587,614

4 Claims. (Cl. Gil-39.75)

This invention relates to smaller gas turbine engines of the type such as are used for propelling marine vessels, automotive trucks, etc., and which differ from the larger gas turbine engines which are used for aircraft propulsion in that, among other distinctions, the smaller engines utilize a centrifugal compressor, axially spaced Unitfid smen Q from the gas turbine, the gas turbine being coupled to the compressor to drive the latter, rather than an axialfiow compressor.

The centrifugal compressor used in the smaller engines described above has advantages of simplicity, ruggedness and low cost, for such smaller gas turbine engines, as compared with the axial flow compressors. This smaller type of engine, with the centrifugal compressor, has certain drawbacks, however, among them, a relatively large diameter for a given air flow capacity, and relatively lower compression efiiciencies than have been obtained heretofore with axial compressors in the larger engines. Moreover, such smaller gas turbine engines have been found in the past to present certain servicing problems, owing to the fact that the combustion chambers have in effect constituted a structural link between the outlets of the compressor and the inlet to the nozzle box which supplies hot gas to the turbines. It has been difficult to get at the combustion chamber, the burner, etc. for servicing, considering the fact that not only was the combustion chamber a structural link between the two parts mentioned, but it was subject to a wide range of temperatures, and consequently there had to be allowance for thermal expansion and contraction, notwithstanding the structural link which the combustion chambers afforded.

The present invention is aimed at improving the overall efliciency of such gas turbines by raising the pressure ratio and the efiiciency of the centrifugal compressors, in order to reduce the fuel consumption of such small gas turbines to values within the range obtained by the large gas turbines with axial compressors, and also to values within a range competitive with piston engines. In addition, by the present invention, the fuel etficiency of the turbine is further raised by a heat exchange arrangement whereby the air, after being compressed, receives heat from the hot gases of combustion, and the latter are in turn cooled down.

In addition, by the design of the present engine, dumping losses, where high velocity vaned passages exit into a larger volume collector, are eliminated by the employment of a series of diffuser pipes of particular proportions in size, and arranged in a particular manner, as between the compressor outlets and a collector chamber which feeds to the combustion chamber.

The engine is improved also in its compactness by the present invention, particularly in the axial direction, and its design is otherwise simplified.

The present invention will be better understood from the following specification taken in connection with the accompanying drawing, which shows in diagrammatic ICE fashion the principles of the invention, and those features which make up the novelty of this invention will be defined in the accompanying claims.

Figure 1 is, in general, an axial sectional view, taken substantially along the plane indicated by the line 11 in Figure 2, illustrating in simplified form the principles of a gas turbine engine constructed according to this invention.

Figure 2 is an isometric view, partly in elevation and partly broken away and shown in axial section.

It will be appreciated that many details are omitted or shown conventionally in the drawings, and that the drawings as a whole are largely diagrammatic in character, to illustrate the principles of the invention, but do not necessarily show a practical construction in all details. Elements such as reduction gearing, bearings, and the like have been omitted, or shown in greatly simplified form, so that the features of novelty will be more clearly apparent.

A centrifugal compressor rotor is represented at 1, supported upon a shaft 10 carried in bearings 11 within a housing 2. The housing is provided with dual annular inlets 21 to the compressor, and completely or interruptedly annular outwardly directed outlet passages 22 lead from the compressor, and have a small number of outlet ports 23 for exit of compressed air.

Axially spaced from the compressor, but coupled thereto, as for instance by being carried upon the same shaft 10, is a primary gas turbine 3. The manner in which air from the compressor is led to a combustion chamber and hot gases from the combustion chamber are led to the turbine 3 constitutes in large part the novelty of the present invention, and will be described in detail shortly. To complete the description of the turbine engine, it may be noted that a secondary gas turbine 4, mounted upon a shaft 40 carried in bearings 41 receives hot gases by way of the passages 42 after the gases have passed through and performed work upon the primary gas turbine wheel 3, and these gases finally exit at 44. The shaft 40 is employed in delivering usable power.

A hollow torus 5 surrounds the gas tubine 3. Internally this torus is divided by a wall 50, which is oriented generally perpendicularly to the axis of the torus and of the shaft, to define within the torus an air collector chamber 51 and a nozzle box 52 for the reception of the hot gases from a combustion chamber or chambers, yet to be described. It will be noted that the compressed air contacts one surface of the dividing wall 50, and the hot gases of combustion contact the opposite surface of that same wall, hence there is an excellent opportunity for heat exchange between the two.

Usually there will be one or more combustion chambers, each consisting of an outer wall 6 of more or less cylindrical form, which is directed preferably in the axial direction, and is mounted at one end only, directly upon the torus 5, and projects from the torus in the axial direction toward the outlets of the compressor 1. This end of the outer wall 6, adjacent the compressor outlet, is left free, but its supported end opens freely to the interior of the collector chamber 51. Within the exterior wall 6, and more or less coaxial therewith, is an inner shell 61, which is perforated and spaced from the outer wall 6 at all points to leave an air chamber 66 between them, which air chamber is, of course, in free communication with the collector chamber 51. The interior of the inner shell 61 constitutes the combustion chamber proper, and this is supported at both ends. At the end corresponding to the supported end of the outer wall 6, the support for the inner shell 61 is in the dividing wall 50, wherefore this end of the inner-shell? opensfreelythrough the wall 50 into the Air for combustion'is conveyed from the outlet ports 23 -of the compressor [to the collector chamberSl by means :of a seriesa of air diffuser pipes-7. These pipes are all of like.size'and'shape .(whic'h simplifies the problem 1of.=:sparei.parts), andwhile they extend generally in the-.axialtdirection, theyare elbowed at 78 for connection to the outlet.ports?23'.l. These-air diffuser pipes, being relativelyrfewin' number, aremade fairly small in diameter, andzof:appreciableslength, expanding quite gradually, in order to avoid dumping losses, mentioned above Their length; is preferablyfive or moretimes the greatest diame ter ofQthe'air diifusertpipe; Such airtdifiuserpipes dis-' chargev directly into the'rtorus, that is into .the collector chamber 51 thereof, at the side nearer the air compressor.

The turbine wheel drives .the compressor 1 in the customary manner, and air admitted at 21 is compressed and centrifugally expelled through the ports 23, and into the individual air diffuser pipes 7, whence it is conveyed with aminimum of expansion to the collector chamber 51, and from the latterit is admitted to the combustion chamber within the inner shell 61, and being mixed with thefuel, burns there, and exits as hot gases of combustion directly into the nozzleboxSZ at the opposite side of the dividing wall 50.- It exits from. the nozzle box through the passages .53 to impingeiupon the blades of the turbine.,.at .3, and thence exits byway of 42 and past the turbine 4, andeout at 44.

The arrangement described provides va sufficient length of diffuser pipe to reduce'dumping losses, yet does not increase the overall length of the engine, nor particularly its diameter. The engine length is determined rather by the space required for the double-inlet compressor, the radial turbine, and the connecting shaft. The entire arrangement is simple and compact, allowing the connecting of Lthe burnersdirectly and simultaneously, both to the air "collector chamber 51 and to the nozzle box 52. Notwithstandingthispthe combustion chamber is left wholly free, atone end at least, andthe burner, admitting to thisend; is readily'accessible. Since thecombustion chamberdoes not constitute a connection between a collector ring and a nozzle box, no'problems of thermal expansion orunduestress are entailed by the free support'of the combustion chamber."

All diffuser pipes can be identical; which simplifies'the passingthrough the air'collector chamber 51, Possibly there will b'e'a slight gain in efi'iciency, since this ordinarilywasted: heat will increase the energy in the air prior to combustiom This .air, it is noted, is already compressed, for:t whereas t: heat added to the airbefore compression causes;Josxof compression'efiiciency; heat added after compressionareducestheamount of fuel required, and improves efli'ciency.

I claim as my invention:

1:"In' aga'sturbine engine, in combination with a cen-- trifugal compressor and an'axially spaced gas turbine coupled thereto, and with a housing for the compressor having outlet ports distributed about the compressor; a hollow torus encircling the gas turbine, a wall dividing said torus generally perpendicularly to its axis into a collector chamber. and a nozzle/box, means defining nozzle, passages leading from thenozzle box to the gas turbine, combustion chambers each comprising an outer wall opening freely at one/end only, to the collector chamber; and a generally coaxialperforated inner shell within-said outer wall and opening, freely-at one end only, to the nozzle box, a burner admitting to the interior of each inner shell, at theendcthereof-udistant from the nozzle box, and means defining circumferentially distributed air passages leading from the outlet ports from the compressor in a generally. axial direction to said collector chamber.

2; In a gasturbine engine, in combination. with a contrifugal compressor and an axiallyspaced gasiturbine coupled'thereto, andwith' a housing for the compressor, having outlet ports distributed about the compressoryaw hollow torus encirclingthegas turbine, a walldividing; said torus generally-perpendicularly to its axis into a col lector chamber and a'n'ozzle ,box, means defining nozzle: passages leading from the nozzle box to the gas turbine a plurality of air diffuser pipes each leading in a generally axial direction 'fr'oma compressor outlet port to" the interior'of said'collector chamber, combustion chambers eachcomprising an outerwall separate from the diffuser pipes,-supported at one'end'only, from the torus," and ex-J tending thence in a generally axial direction, and openingfreely into the collector chamber, and a generally coaxial perforated inner shell supported at one end fromsa'id dividing wall, and opening freely into the nozzle box,'and" a burner admittingto the interior of said innershelh'at" the end thereof distant from the nozzle box:

3; In a gas turbine engine, in combination withacem trifugal compressor and an axially spaced gas turbine'coupled thereto, and with a housing for the compressor formed withl'angularly spaced outlet ports distributed" about and leading from'the'compressor; a hollow torus encircling the gas. turbine, a wall dividing said torus gen-- erally perpendicularlyxto its axis into a collectorchamber at the side nearer the compressor, and a nozzle box at the opposite side, means defining gas passages-leading from the 'nozzletboxinwardly to the turbine,.a,plurality of elbowed air diifuser pipes, one for each compressoroutlet port, extending first outwardly therefromandathen' generally in the axial direction, and connected for;dis

charge into said collector chamber, combustion chambers supported upon said torus andextending generally inflthe axial direction, each including a perforated inner: shell dividing the inner combustion space from a surrounding: air supply chamber, said air supply chamber beingin' freer: communication at one endiwith the collector chamber, and the inner combustion-space being in free communion-1r tion vatthe same .end with. the nozzlebox, and .a burner-" admitting to the interior of saidtcombustion space:

4.- Thecombination .of claim 3,Wi1l6ll1' the air difr'user w pipesare gradually enlarged in internal diameter'fromr: the compressor outlet port to the'discharge ;end at the collector chamber, and are of a length at least five times their maximum diameter.

References .Cited. in the file of this patent UNITED STATES PATENTS" 

